Diurnal and seasonal cold lands signatures in SSM/I-scale microwave radiometry of the North Slope of Alaska

Data assimilation of satellite remote sensing observations into hydrologic and meteorological models holds great promise for our ability to estimate and understand a variety of land surface process parameters. Near-surface soil temperature and moisture (quantity and frozen/thawed state) conditions are the most basic parameters needed, and microwave radiometry offers several advantages over other approaches. Radiometry is directly sensitive to temperature and moisture conditions, solar illumination is not required, and clouds do not prevent observations. These are even greater advantages in the climatologically and ecologically sensitive arctic where climate changes are expected to be strongest and to be evident earliest. However, satellite radiometers such as the Special Sensor Microwave/Imager (SSM/) have relatively coarse spatial resolution (10s of km). And, when the area within a footprint is not homogeneous, disaggregation becomes a major issue. Thus, for example, it can be difficult to study the performance of assimilation techniques in mid-latitude areas. This study expands on our earlier Radiobrightness Energy Balance Experiment-3 (REBEX-3), which featured a tower-based SSM/I simulator deployed on the North Slope of Alaska in 1994-95. In that study, a comparison of tower and satellite signatures at 19 & 37 GHz strongly suggested that the North Slope is radiometrically homogeneous for spatial scales up to SSM/I footprints-an unusual and valuable characteristic that could be exploited for assimilation studies. Here we examine the SSM/I signatures of five North Slope sites.